Try connecting to the SCX-3405W via USB and and the Samsung Easy Printer 
Manager (SEPM) software. Under Device Settings / Network at the bottom of 
the page there is a Restore Defaults, Network Settings Clear button, which 
also clears the security config, resetting in back to admin/ sec00000. Then 
power the printer off then back on. You'll then need to re-instate the 
network settings which can be done via the SEPM software.